WO2017140484A1 - Electric machine and configuration method - Google Patents

Electric machine and configuration method Download PDF

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Publication number
WO2017140484A1
WO2017140484A1 PCT/EP2017/051941 EP2017051941W WO2017140484A1 WO 2017140484 A1 WO2017140484 A1 WO 2017140484A1 EP 2017051941 W EP2017051941 W EP 2017051941W WO 2017140484 A1 WO2017140484 A1 WO 2017140484A1
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WO
WIPO (PCT)
Prior art keywords
stator
electric machine
teeth
equation
rotor poles
Prior art date
Application number
PCT/EP2017/051941
Other languages
French (fr)
Inventor
Istvan Kiraly
Alexandros MICHAELIDES
Original Assignee
Jaguar Land Rover Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Jaguar Land Rover Limited filed Critical Jaguar Land Rover Limited
Priority to DE112017000826.3T priority Critical patent/DE112017000826T5/en
Priority to US16/074,036 priority patent/US20190044396A1/en
Publication of WO2017140484A1 publication Critical patent/WO2017140484A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/14—Stator cores with salient poles
    • H02K1/146—Stator cores with salient poles consisting of a generally annular yoke with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/14—Stator cores with salient poles
    • H02K1/141—Stator cores with salient poles consisting of C-shaped cores
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/14—Stator cores with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K41/00—Propulsion systems in which a rigid body is moved along a path due to dynamo-electric interaction between the body and a magnetic field travelling along the path
    • H02K41/02—Linear motors; Sectional motors
    • H02K41/03—Synchronous motors; Motors moving step by step; Reluctance motors
    • H02K41/031—Synchronous motors; Motors moving step by step; Reluctance motors of the permanent magnet type
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K15/00—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
    • H02K15/02—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies
    • H02K15/021—Magnetic cores
    • H02K15/022—Magnetic cores with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K15/00—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
    • H02K15/02—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies
    • H02K15/03—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies having permanent magnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K21/00—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets
    • H02K21/12—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with stationary armatures and rotating magnets
    • H02K21/14—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with stationary armatures and rotating magnets with magnets rotating within the armatures
    • H02K21/16—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with stationary armatures and rotating magnets with magnets rotating within the armatures having annular armature cores with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K2201/00—Specific aspects not provided for in the other groups of this subclass relating to the magnetic circuits
    • H02K2201/15—Sectional machines
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K2213/00—Specific aspects, not otherwise provided for and not covered by codes H02K2201/00 - H02K2211/00
    • H02K2213/03—Machines characterised by numerical values, ranges, mathematical expressions or similar information

Definitions

  • the base model may have the following configuration :
  • a sector angle a of the one or more cut-out sector may be defined by the equation:
  • the stator comprises one or more cut-out segment.
  • This arrangement has particular application where limited space is available for the electric machine.
  • the packaging constraint may, for example, be the result of packaging a clutch mechanism or other mechanical device, such as a power split device, in close proximity to the electric machine.
  • the diameter of the rotor may be increased (compared to an electric machine having an annular stator). At least in certain embodiments, this may provide a higher maximum torque.
  • the teeth/pole ratio may be lower than 3/2 which is conventional for concentrated winding machines. This may enable higher torque density or lower current density values.
  • N p is the number of rotor poles
  • k is a non-negative integer (0, 1 , 2, 3...);
  • f is a positive integer (1 , 2, 3).
  • stator teeth 9 The number of stator teeth 9 is calculated using the equation:
  • N t N tBase ⁇ f [Equation 2] Where: N t is the number of stator teeth ;
  • N tBase is the number of stator teeth in the base model
  • f is a positive integer (1 , 2, 3).
  • k is a non-negative integer (0, 1 , 2, 3...);
  • k is a non-negative integer (0, 1 , 2, 3...);
  • the sector angle a of the minor annular sector is 27.7°, such that the angular extent of the major annular sector is 332.3 ° (360°- a).
  • the angular pitch ⁇ of the teeth 9 in the stator 4 is 12.3 °.
  • the configuration of the stator teeth 9 and the rotor poles 12 of the electric machine 1 is such that magnetic imbalance may be reduced.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Electromagnetism (AREA)
  • Manufacturing & Machinery (AREA)
  • Iron Core Of Rotating Electric Machines (AREA)

Abstract

The present disclosure relates to a method of configuring an electric machine (1). The electric machine (1) has a rotor (5) having N p rotor poles (12), where N p is the number of rotor poles (12); and a stator (4) having one or more cut-out sector and N t stator teeth (9), where N t is the number of stator teeth (9). The electric machine (1) is configured in dependence on a base model (Base1) having N tBase stator teeth (9) and N pBase rotor poles (12), where N tBase and N pBase are both integers greater than one and N pBase is an odd number. The method includes calculating N p using the equation (I) and calculating N t using the equation (II); Where: N p is the number of rotor poles (12) and is greater than one; N t is the number of stator teeth (9) and is greater than one; N pBase is the number of rotor poles (12) in the base model; N tBase is the number of stator teeth (9) in the base model; k is a non-negative integer; and f is a positive integer. The present disclosure also relates to an electric machine (1) having a topology configured according to these equations. Furthermore, the present disclosure relates to a vehicle (2) including said electric machine (1).

Description

ELECTRIC MACHINE AND CONFIGURATION METHOD
TECHNICAL FIELD
The present disclosure relates to an electric machine and configuration method. More particularly, but not exclusively, the present disclosure relates to a method of configuring an electric machine; and to an electric machine for use in a vehicle. The present disclosure also relates to a vehicle including an electric machine.
BACKGROUND
It is known to provide an electric machine in a vehicle to generate a tractive force for propelling the vehicle. The electric machine typically includes a stator and a rotor. The electric machine may be the sole means of propulsion for the vehicle, or may be used in conjunction with another torque generating machine, such as an internal combustion engine. In certain applications there may be constraints on the available packaging space for the electric machine. It may not be possible for the stator to have a complete annular configuration (i.e. extending through 360 °). However it is desirable to use the maximum available rotor diameter to develop the maximum torque. One possible application where packaging limitations may arise is a hybrid electric vehicle in which the electric machine may be disposed in a housing of a transmission coupled to an internal combustion engine. In this application, external devices may impinge on to the transmission housing, thereby reducing the available volume in the transmission housing to accommodate the electric machine.
It is known from the applicant's earlier applications GB1303653.8 and PCTPCT/EP2013/074280 to provide an electric machine having a stator formed from a plurality of segments. The segments may be configured to form a part-annular stator. In one configuration, the stator is C-shaped in order to increase the volume of the electric machine.
A potential shortcoming of electric machines having a part-annular stator is that certain rotor and stator configurations have an electromagnetic imbalance. This imbalance may limit the number of possible options for connect the coils. In turn, this may affect manufacturability of the electric machine.
At least in certain embodiments, the present invention seeks to provide a method and apparatus which overcomes some of the aforementioned shortcomings.
SUMMARY OF THE INVENTION Aspects of the present invention relate to a method of configuring an electric machine, an electric machine, and to a vehicle as claimed in the appended claims.
According to an aspect of the present invention there is provided a method of configuring an electric machine (1 ),
the electric machine (1 ) comprising:
a rotor (5) having Np rotor poles (12), where Np is the number of rotor poles (12); and
a stator (4) having one or more cut-out sector and Nt stator teeth (9), where Nt is the number of stator teeth (9);
the method comprising configuring the electric machine (1 ) in dependence on a base model (Basel ) having NtBase stator teeth (9) and NpBase rotor poles (12), where NtBase and NpBase are both integers greater than one and NpBase is an odd number;
wherein Np is calculated using the equation:
1 - (-1)/
Np = - + 2 ■ k + NpBase ■ f and Nt is calculated using the equation: Nt = NtBase ■ f
Where: Np is the number of rotor poles (12) and is greater than one;
Nt is the number of stator teeth (9) and is greater than one;
NpBase is the number of rotor poles (12) in the base model;
NtBase is the number of stator teeth (9) in the base model;
k is a non-negative integer; and
f is a positive integer.
This method facilitates determination of the parameters of the electric machine, such as the topology of the rotor and stator, in dependence on a base model. The number of stator teeth and rotor poles are determined. At least in certain embodiments, the method allows the magnetic balance of the electric machine to be optimised. The topologies derived from this method are usable in packages where a prior art electric machine having an arcuate stator extending through 360° could not be used, for example due to packaging constraints. The stator includes one (or more) cut-out sector(s) and, in transverse section, has a part- annular configuration occupying less than 360°. This arrangement enables implementation of the electric machine in package-restricted applications. The method may comprise calculating a sector angle a of the one or more cut-out sector(s) using the equation:
1 _ -iy
—T^+ 2'k
a = i - (-1) 360
2 + 2■ k + NpBase ' f
Where: a is the sector angle of the cut-out sector in the stator. The method facilitates calculation of the sector angle of the cut-out sector and may help to define appropriate teeth-pole combinations for the electric machine.
The method may comprise calculating an angular pitch β of the teeth in the stator using the equation:
360 - a
β = -Γ ι
J ' N tease
Where: β is the angular pitch of teeth in the stator.
The angular pitch β is the angle between adjacent teeth in the stator. It will be understood that the angular pitch of teeth is not an integer multiple of 360°. Accordingly, there is no equivalent configuration of an electric machine having an arcuate stator extending through 360° (i.e. without a sector cut-out).
The base model may have the following configuration:
NtBase = 6; and
NpBase = 5.
According to a further aspect of the present invention there is provided an electric machine comprising a rotor and a stator, the stator having a sector cut-out; wherein the electric machine is configured in dependence on a base model having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpBase is an odd number;
the rotor having Np rotor poles, wherein Np is defined by the equation: 1 - {-i)f
Np = - + 2■ k + NpBase ■ f
2 the stator having Nt stator teeth, where Nt is defined by the equation:
Nt = NtBase ■ f
Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NVBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
The stator includes one or more cut-out sector and, therefore, has a part-annular configuration which occupies less than 360°. This arrangement enables implementation of the electric machine in package-restricted applications. This is only valid for certain topologies and combinations of stator and rotor poles. A sector angle a of the one or more cut-out sector may be defined by the equation: i _ -iy
— T^ + 2 ' k
a = i - (-1) 360
2 + 2■ k + NpBase ■ f
Where: a is the sector angle of the cut-out sector in the stator.
An angular pitch β of the teeth in the stator may be defined by the equation:
360 - a
β =
f ' NtBase
Where: β is the angular pitch of teeth in the stator.
The base model may have the following configuration:
NtBase = 6; and
NpBase = 5. The non-negative integer k may be one (k=1 ); and the positive integer f may be three (f=3). The stator may have eighteen stator teeth; and the rotor may have eighteen (18) poles. The sector angle a of the one or more cut-out sector may be 60 °. If the stator comprises more than one cut-out sector, the sector angle a defines the combined angular extent of said cut- out sectors. The angular pitch β of the teeth in the stator may be 16.67°.
The stator can be segmented into one or more segments. The one or more segment may each have a self-contained flux path. The tooth number values of each segment could be eighteen (18), nine (9), six (6) or two (2). The design has particular details that enable better modular design. The dimensions of the segments may be configured to reduce torque ripple and voltage harmonics.
The stator comprises one or more cut-out segment. This arrangement has particular application where limited space is available for the electric machine. For example, when installed in a vehicle or the like, there may be packaging constraints which impinge on or limit the available space for the electric machine. The packaging constraint may, for example, be the result of packaging a clutch mechanism or other mechanical device, such as a power split device, in close proximity to the electric machine. By including one or more cut-out segment in the stator, the diameter of the rotor may be increased (compared to an electric machine having an annular stator). At least in certain embodiments, this may provide a higher maximum torque. Furthermore, there may be more space available for coils on the stator teeth. The teeth/pole ratio may be lower than 3/2 which is conventional for concentrated winding machines. This may enable higher torque density or lower current density values.
According to a further aspect of the present invention there is provided a method of configuring an electric machine (1 ),
the electric machine (1 ) comprising:
a rotor (5) having Np rotor poles (12), where Np is the number of rotor poles (12) and is greater than one; and
a stator (4) having one or more cut-out sector and Nt stator teeth (9), where Nt is the number of stator teeth (9) and is greater than one;
the method comprising configuring the electric machine (1 ) in dependence on a base model (Base2) having NtBase stator teeth (9) and NpBase rotor poles (12), where NtBase and NpBase are both integers greater than one and NpBase is an even number;
wherein Np is calculated using the equation: Np = (2 ■ k + Npbase ■ f) and Λ/f is calculated using the equation :
Nt = NtBase ■ f
Where: Np is the number of rotor poles (1 2) and is greater than one;
Nt is the number of stator teeth (9) and is greater than one;
NpBase is the number of rotor poles (12) in the base model;
NtBase is the number of stator teeth (9) in the base model;
k is a non-negative integer; and
f is a positive integer.
The method may comprise calculating a sector angle a of the one or more cut-out sector using the equation :
2 - k
a =—— ■ 360
2 1 k + Npftase 1 f
Where: a is the sector angle of the cut-out sector in the stator.
The method may comprise calculating an angular pitch β of the teeth in the stator using the equation :
360 - a
β =
f ' NtBase
Where: β is the angular pitch of teeth in the stator.
The base model may have the following configuration :
NtBase = 9; and
NpBase = 8.
According to a further aspect of the present invention there is provided an electric machine comprising a rotor and a stator, the stator having a sector cut-out; wherein the electric machine is configured in dependence on a base model having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpB; number;
the rotor having Np rotor poles, wherein Np is defined by the equation:
Np = (2■ k + Npbase ■ f) the stator having Nt stator teeth, where Nt is defined by the equation:
Nt = NtBase ■ f
Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NpBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
A sector angle a of the one or more cut-out sector may be defined by the equation:
2■ k + Npi)ase ' f
Where: a is the sector angle of the cut-out sector in the stator. An angular pitch β of the stator teeth 9 is defined by the equation:
360 - a
f ' tBase
Where: β is the angular pitch of teeth in the stator.
The stator comprises one or more cut-out segment. This arrangement has particular application where limited space is available for the electric machine. For example, when installed in a vehicle or the like, there may be packaging constraints which impinge on or limit the available space for the electric machine. The packaging constraint may, for example, be the result of packaging a clutch mechanism or other mechanical device, such as a power split device, in close proximity to the electric machine. By including one or more cut-out segment in the stator, the diameter of the rotor may be increased (compared to an electric machine having an annular stator). At least in certain embodiments, this may provide a higher maximum torque. Furthermore, there may be more space available for coils on the stator teeth. The teeth/pole ratio may be lower than 3/2 which is conventional for concentrated winding machines. This may enable higher torque density or lower current density values.
The base model (Base 2) may have the following configuration:
NtBase = 9; and
NpBase = 8.
According to a further aspect of the present invention there is provided a vehicle comprising an electric machine as described herein. The electric machine may be a traction motor for generating a tractive force to propel the vehicle.
Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.
BRIEF DESCRIPTION OF THE DRAWINGS
One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:
Figure 1 shows a schematic representation of a vehicle incorporating an electric machine in accordance with an embodiment of the present invention;
Figure 2 shows a sectional view of the electric machine shown in Figure 1 ; and Figure 3 shows a first coil topology of the windings on the stator of the electric machine shown in Figure.
DETAILED DESCRIPTION An electric machine 1 in accordance with embodiments of the present invention will now be described by way of example. As illustrated in Figure 1 , the electric machine 1 has particular application in a vehicle 2 to generate a traction force. The electric machine 1 can operate in the traction mode to provide the sole tractive force for propelling the vehicle, for example an electric vehicle (EV); or in conjunction with the internal combustion engine, for example a hybrid electric vehicle (HEV).
With reference to Figure 2, the electric machine 1 is a permanent magnet synchronous motor (PMSM). The electric machine 1 is a three-phase machine in the present embodiment. The electric machine 1 comprises a stator 4 and a rotor 5. The rotor 5 is configured to rotate about a longitudinal axis X of the electric machine 1 (extending perpendicular to the plane of the page on Figure 2). The electric machine 1 is described herein with reference to a transverse cross-section disposed perpendicular to said longitudinal axis X. The electric machine 1 is installed within a component housing 6, such as a transmission housing, of the vehicle 2. The component housing 6 defines a chamber 7 for the electric machine 1 . A protuberance 8 projects inwardly into the chamber 7. The remainder of the chamber 7 has a circular profile in transverse cross-section. The protuberance 8 can, for example, be formed by one or more assembly or machine, such as a power transfer unit or a starter motor, which may be disposed within the chamber 7 or adjacent to the component housing 6.
The stator 4 has a part-annular profile in transverse cross-section. Specifically, the stator 4 consists of a major annular sector in transverse cross-section. The corresponding minor annular sector is an annular gap formed in the stator 4 to accommodate the protuberance 8. Thus, in transverse cross-section, the stator 4 is generally C-shaped and comprises first and second ends 4-1 , 4-2 which are separated from each other. As described herein, the angular extent of the major and minor annular sectors is defined to accommodate the protuberance 8. The stator 4 is formed from a plurality of laminations arranged in face-to-face contact with each other to form a stacked core. The laminations can, for example, be made of electrical steel.
The stator 4 comprises a plurality of stator teeth 9 projecting radially inwardly from a radially outer part-annular segment 10. The stator 4 in the present embodiment extends over 300 ° and comprises eighteen (18) stator teeth 9. The stator teeth 9 are labelled 9-1 through 9-18 in a counter-clockwise direction starting from the first end 4-1 of the stator 4. The stator teeth 9 have an angular spacing (pitch) of 16.67°. Unlike fully swept electric machines (i.e. electric machines having a stator extending over 360 °), the angle between the stator teeth 9 is not an integer multiple of 360°. The stator 4 can be formed from one or more segments provided the resulting flux paths are self-contained within each segment. The number of stator teeth 9 in each segment may, for example, be eighteen (18) (as illustrated in Figure 2), six (6) or two (2). It will be appreciated, therefore, that the stator 4 may have a modular design. The dimensions of each segment can be modified to reduce torque ripple and voltage harmonics.
The rotor 5 has a substantially circular transverse cross-section and is arranged coaxially with the stator 4. The rotor 5 comprises eighteen (18) permanent magnets which form rotor poles 12 having uniform angular spacing around the rotor 5. Thus, the rotor pole pitch is 20° in the present embodiment. The rotor poles 12 are each formed by one or more permanent magnets. The rotor poles 12 can, for example, be made of rare-earth materials to provide a high density of magnetic flux. The stator teeth 9 carry windings 1 1 connected to the 3-phase supply. In the present embodiment the windings 1 1 are concentrated windings comprising separate coils wound on each stator tooth 9. The phase shift between the windings 1 1 is 150 electrical degrees. If the windings 1 1 of two adjacent slots are in the same phase, then these windings 1 1 are connected with opposite polarity, resulting in a phase shift of 30 electrical degrees. At least in certain embodiments this can enable a higher torque density and/or a lower current density. With reference to Figure 3, the first coil topology [T1 ] of the windings 1 1 is as follows:
-A -B +B +C -C -A +A +B -B -C +C +A -A -B +B +C -C -A [T1 ]
It will be understood that the first coil topology [T1 ] defines the phase of the current supplied to the stator teeth 9-1 to 9-18 in a counter-clockwise direction starting from the first end 4-1 of the stator 4. With reference to Figure 1 , the windings 1 1 are electrically coupled to a high voltage (HV) battery 14 via a first inverter 15. A control unit 16 comprising a first electronic controller (not shown) is provided for sequencing the supply of current to the windings 1 1 . The interaction of the current in the windings 1 1 and the magnetic flux generated by the permanent magnets in the rotor poles 12 cause the rotor 5 to rotate. The supply sequence is the same as a conventional three (3) phase PMSM having a circular stator. Thus, the electric machine 1 operates in a conventional manner.
With reference to Figure 2, a circumferential shield element 17 extends between the ends of the stator 4 to reduce the transmittal of magnetic flux from the rotor poles 12 into the component housing 6. However, the first and second ends 4-1 , 4-2 of the stator 4 are magnetically isolated and this can result in voltage imbalances within the electric machine 1 .
At least in certain embodiments the configuration of the stator 4 helps to reduce the volume of the stator teeth 9 and to lower the back-EMF harmonic content (compared to an equivalent 3/2 topology). The stator 4 may also lower the motor frequency by up to 10% (compared to a known fractional slot topology); and reduce the voltage imbalance in back- EMF of the windings 1 1 belonging to the same phase (compared to an equivalent 3/2 topology).
The methodology for determining the pole/slot combination of the electric machine 1 to reduce magnetic imbalance will now be described. The term Np defines the number of rotor poles; and the term Nt defines the number of stator teeth. A first base model (Basel ) and a second base model (Base 2) are defined and form the basis of higher pole/slot combinations for the electric machine 1 . The first base model has a 6/5 (stator teeth/rotor pole) configuration (i.e. NtBasel = 6/NpBasel = 5) ; and the second base model has a 9/8 (stator teeth/rotor pole) configuration (i.e. NtBase2 = 9/NpBase2 = 8). As described below, the first base model forms the basis of the electric machine 1 which is illustrated in Figure 2 having eighteen (18) stator teeth 9 and eighteen (18) rotor poles 12. It will be understood that additional base models may be defined.
In respect of base models having an odd number of rotor poles 12 (for example, NpBase = 5, 7, 9 ...), the following set of equations (Equations 1 to 4) are applied. The number of rotor poles (Np) in the electric machine 1 is calculated by applying the equation:
Np = ^ ^- + 2 - k + NpBase ■ f [Equation 1 ]
Where: Np is the number of rotor poles;
NpBase is the number of rotor poles in the base model;
k is a non-negative integer (0, 1 , 2, 3...); and
f is a positive integer (1 , 2, 3...).
The number of stator teeth 9 is calculated using the equation:
Nt = NtBase ■ f [Equation 2] Where: Nt is the number of stator teeth ;
NtBase is the number of stator teeth in the base model; and
f is a positive integer (1 , 2, 3...).
An sector angle a of the minor annular (cut-out) sector forming a cut-out in the stator 4 is calculated using the equation :
« = T T H 360 [Equation 3]
+2-k+NpBase-f
2
Where: NpBase is the number of rotor poles in the base model;
k is a non-negative integer (0, 1 , 2, 3...); and
f is a positive integer (1 , 2, 3...). Furthermore, the angular pitch β of the stator teeth 9 (i.e. the angle between adjacent stator teeth 9) is calculated using the equation : 360- a r l_ ..
β = — [Equation 4]
J 'NtBase where NtBase is the number of stator teeth in the base model; and
f is a positive integer (1 , 2, 3...).
It will be understood that, in order to determine the configuration of the electric machine 1 , the non-negative integer k and the positive integer f are constant for each equation. As outlined above, equations 1 to 4 are applied for a base model consisting of an odd number of stator teeth 9, such as the first base model (Basel ) having a 6/5 (stator teeth/rotor pole) configuration. By way of example, if the non-negative integer k is set as one (/ =1 ) and the positive integer f is set as three (f=3), the application of equations 1 to 4 using the first base model having a 6/5 (stator teeth/rotor pole) configuration (i.e. NtBasel = 6/NpBasel = 5) results in the electric machine 1 illustrated in Figure 2. Specifically, the stator 4 has eighteen (18) stator teeth 9 (Nt = 18) ; and the rotor 5 has eighteen (18) rotor poles 12. The sector angle a of the minor annular sector is 60 °, such that the angular extent of the major annular sector is 300 ° (360 °- a). The angular pitch β of the teeth 9 in the stator 4 is 16.67°. The configuration of the stator teeth 9 and the rotor poles 12 of the electric machine 1 is such that magnetic imbalance may be reduced.
In respect of base models having an even number of rotor poles (for example, NpBase = 8, 10, 12 ...), the following set of equations (Equations 5 to 8) are applied. The number of rotor poles (Np) is calculated by applying the equation:
Np = (2■ k + Npbase ■ f) [Equation 5]
Where: Np is the number of rotor poles;
NpBase is the number of rotor poles in the base model;
k is a non-negative integer (0, 1 , 2, 3...); and
f is a positive integer (1 , 2, 3...). If the non-negative integer k is set as zero (k=0), the electric machine 1 has an arcuate stator 4 extending over 360° (i.e. without a minor annular sector cut-out). The integer k may be specified as a positive integer (i.e. k>0) for an electric machine 1 having a part-arcuate stator 4. The number of stator teeth 9 is calculated using the equation:
Nt = Nt tBase ■ f [Equation 6]
Where: Nt is the number of stator teeth;
NtBase is the number of stator teeth in the base model; and
f is a positive integer (1 , 2, 3...).
An sector angle a of the minor annular (cut-out) sector forming a cut-out in the stator 4 is calculated using the equation:
2-k
a = 360 [Equation 7]
2-k+Npbase-f ^
Where: NpBase is the number of rotor poles in the base model;
k is a non-negative integer (0, 1 , 2, 3...); and
f is a positive integer (1 , 2, 3...). Furthermore, the angular pitch β of the stator teeth 9 is calculated using the equation:
360- β = [Equation 8]
f'NtBase where NtBase is the number of stator teeth in the base model; and
f is a positive integer (1 , 2, 3...).
It will be understood that, in order to determine the configuration of the electric machine 1 , the non-negative integer k and the positive integer f are constant for each equation. As outlined above, equations 5 to 8 are applied for a base model consisting of an even number of stator teeth 9, such as the first base model (Base2) having a 9/8 (stator teeth/rotor pole) configuration. By way of example, if the non-negative integer k is set as one (/c=1 ) and the positive integer f is set as three (f=3), the application of equations 5 to 8 using the second base model having a 9/8 (stator teeth/rotor pole) configuration (i.e. NtBasel = 9/NpBasel = 8) results in an electric machine 1 having twenty-seven (27) stator teeth 9 (Nt = 27) ; and the rotor 5 has twenty-six (26) rotor poles 12 (Np = 26). The sector angle a of the minor annular sector is 27.7°, such that the angular extent of the major annular sector is 332.3 ° (360°- a). The angular pitch β of the teeth 9 in the stator 4 is 12.3 °. The configuration of the stator teeth 9 and the rotor poles 12 of the electric machine 1 is such that magnetic imbalance may be reduced.
The present disclosure extends to electric machines 1 having stator teeth 9 and rotor poles 12 configurations which comply with the sets of equations outlined above in respect of the first and second base models.
It will appreciated that further changes can be made to the electric machine 1 described herein without departing from the scope of the present invention.

Claims

CLAIMS:
1 . A method of configuring an electric machine,
the electric machine comprising:
a rotor having Np rotor poles, where Np is the number of rotor poles; and a stator having one or more cut-out sector and Nt stator teeth, where Nt is the number of stator teeth;
the method comprising configuring the electric machine in dependence on a base model (Basel ) having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpBase is an odd number;
wherein Np is calculated using the equation:
1 - (-1)
Np = + 2 ■ k + NpBase ■ f and Nt is calculated using the equation:
Nt = NtBase ■ f
Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NpBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
2. A method as claimed in claim 1 comprising calculating a sector angle a of the one or more cut-out sector using the equation:
Where: a is the sector angle of the cut-out sector in the stator.
3. A method as claimed in claim 2 comprising calculating an angular pitch β of the teeth in the stator using the equation:
360 - a
β =
f ' N tBase
Where: β is the angular pitch of teeth in the stator.
4. A method as claimed in any one of claims 1 , 2 or 3, wherein the base model has the following configuration:
NtBase = 6; and
NpBase = 5.
5. An electric machine comprising a rotor and a stator, the stator having a sector cutout; wherein the electric machine is configured in dependence on a base model having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpBase is an odd number;
the rotor having Np rotor poles, wherein Np is defined by the equation:
1 - (-1)
Np = + 2 ■ k + NpBase ■ f the stator (4) having Nt stator teeth (9), where Nt \s defined by the equation:
Nt = NtBase ■ f Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NpBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
6. An electric machine as claimed in claim 5, wherein a sector angle a of the one or more cut-out sector is defined by the equation: —T~^+ 2'k
a = i - (-1) 360
2 + 2■ k + NpBase ' f
Where: a is the sector angle of the cut-out sector in the stator.
7. An electric machine as claimed in claim 6, wherein an angular pitch β of the teeth in the stator is defined by the equation:
360 - a
β = J- N ^tBase Where: β is the angular pitch of teeth in the stator.
8. An electric machine as claimed in any one of claims 5, 6 or 7, wherein the base model (Basel ) has the following configuration:
NtBase = 6; and
NpBase = 5.
9. An electric machine as claimed in claim 8, wherein the non-negative integer k is one (k=1 ) and the positive integer f is three (f=3), the stator having eighteen stator teeth; and the rotor having eighteen poles.
10. An electric machine as claimed in claim 9 when dependent directly or indirectly on claim 6, wherein the sector angle a of the one or more cut-out annular sector is 60°.
1 1 . An electric machine as claimed in claim 9 or claim 10 when dependent directly or indirectly on claim 7, wherein the angular pitch β of the teeth in the stator is 16.67°.
12. A method of configuring an electric machine,
the electric machine comprising:
a rotor having Np rotor poles, where Np is the number of rotor poles and is greater than one; and
a stator having one or more cut-out sector and Nt stator teeth, where Nt is the number of stator teeth and is greater than one; the method comprising configuring the electric machine in dependence on a base model (Base2) having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpBase is an even number;
wherein Np is calculated using the equation :
Np = (2 ■ k + Npbase ■ f) and Λ/f is calculated using the equation : Nt = NtBase - f
Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NpBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
1 3. A method as claimed in claim 12 comprising calculating a sector angle a of the one or more cut-out sector using the equation :
2 - k
a =—— ■ 360
2 1 k + Npftase 1 f
Where: a is the sector angle of the cut-out sector in the stator.
14. A method as claimed in claim 13 comprising calculating an angular pitch β of the teeth in the stator using the equation :
360 - a
β =
f ' NtBase
Where: β is the angular pitch of teeth in the stator.
1 5. A method as claimed in any one of claims 12 to 14, wherein the base model (Base 2) has the following configuration: NtBase = 9; and
NpBase = 8.
16. An electric machine comprising a rotor and a stator, the stator having a sector cutout; wherein the electric machine is configured in dependence on a base model having NtBase stator teeth and NpBase rotor poles, where NtBase and NpBase are both integers greater than one and NpBase is an even number;
the rotor having Np rotor poles, wherein Np is defined by the equation:
Np = (2■ k + Npbase ■ f) the stator having Nt stator teeth, where Nt is defined by the equation:
Nt = NtBase ■ f
Where: Np is the number of rotor poles and is greater than one;
Nt is the number of stator teeth and is greater than one;
NpBase is the number of rotor poles in the base model;
NtBase is the number of stator teeth in the base model;
k is a non-negative integer; and
f is a positive integer.
17. An electric machine as claimed in claim 5, wherein a sector angle a of the one or more cut-out sector is defined by the equation:
2 - k
a =—— -■ 360
L■ k + Npbase ' J
Where: a is the sector angle of the cut-out sector in the stator.
18. An electric machine as claimed in claim 6, wherein an angular pitch β of the teeth the stator is defined by the equation:
360 - a
f - Nt tBase Where: β is the angular pitch of teeth in the stator.
19. An electric machine as claimed in any one of claims 16 to 18, wherein the base model (Base 2) has the following configuration:
NtBase = 9; and
NpBase = 8.
20. A vehicle comprising an electric machine as claimed in any one of claims 5 to 1 1 ; or any one of claims 16 to 19.
21 . A method of configuring an electric machine substantially as herein described with reference to the accompanying figures.
22. An electric machine substantially as herein described with reference to the accompanying figures.
23. A vehicle substantially as herein described with reference to the accompanying figures.
PCT/EP2017/051941 2016-02-15 2017-01-30 Electric machine and configuration method WO2017140484A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002345224A (en) * 2001-05-18 2002-11-29 Yaskawa Electric Corp Permanent-magnet synchronous motor
GB2518689A (en) * 2013-09-30 2015-04-01 Jaguar Land Rover Ltd Electric machine

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1303653A (en) 1969-02-14 1973-01-17
GB2511353B (en) * 2013-03-01 2015-11-04 Jaguar Land Rover Ltd Electric machine having segmented stator with shield elements
US10224767B2 (en) 2012-11-20 2019-03-05 Jaguar Land Rover Limited Electric machine and method of operation thereof
GB2518688B (en) * 2013-09-30 2016-10-19 Jaguar Land Rover Ltd Electric machine and method of operation thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002345224A (en) * 2001-05-18 2002-11-29 Yaskawa Electric Corp Permanent-magnet synchronous motor
GB2518689A (en) * 2013-09-30 2015-04-01 Jaguar Land Rover Ltd Electric machine

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DE112017000826T5 (en) 2018-10-25
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GB201602630D0 (en) 2016-03-30
GB2547422A (en) 2017-08-23

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